Molten bath smelting or other pyro-metallurgical operations that require interaction between the bath and a source of oxygen-containing gas utilize several different arrangements for the supply of the gas. In general, these operations involve direct injection into molten matte/metal. This may be by bottom blowing tuyeres as in a Bessemer type of furnace or side blowing tuyeres as in a Peirce-Smith type of converter. Alternatively, the injection of gas may be by means of a lance to provide either top blowing or submerged Injection. Examples of top blowing lance injection are the KALDO and BOP/BOF steel making plants in which pure oxygen is blown from above the bath to produce steel from molten iron. Another example is provided by the Mitsubishi copper process, in which injection lances cause jets of oxygen-containing to be provided in the smelting and matte converting stages so as to impinge on and penetrate the top surface of the bath, respectively to produce and to convert copper matte. In the case of submerged lance injection, the lower end of the lance is submerged so that injection occurs within rather than from above a slag layer of the bath, to provide top submerged lancing injection, of which a well know example is the Outotec AUSMELT top submerged lancing technology that is applied to a wide range of metals processing.
With both forms of injection from above, that is, with both top blowing and top submerged lancing injection, the lance is subjected to intense prevailing bath temperatures. The top blowing in the Mitsubishi copper process uses a number of relatively small steel lances that have an inner pipe of about 50 mm diameter and an outer pipe of about 100 mm diameter. The inner pipe terminates at about the level of the furnace roof, well above the reaction zone. The outer pipe is rotatable to prevent it sticking to a water-cooled collar at the furnace roof, and it extends down into the gas space of the furnace to position its lower end about 500-800 mm above the upper surface of the molten bath. Particulate feed entrained in air is blown through the inner pipe, while oxygen enriched air is blown through the annulus between the pipes. Despite the spacing of the lower end of the outer pipe above the bath surface, and any cooling of the lance by the gases passing through it, the outer pipe burns back by about 400 mm per day. The outer pipe therefore is slowly lowered and, when required, new sections are attached to the top of the outer, consumable pipe.
The lances for top submerged lancing injection are much larger than those for top blowing, such as in the Mitsubishi process described above. A top submerged injecting lance usually has at least an inner and an outer pipe, as assumed in the following, but may have at least one other pipe concentric with the inner and outer pipes. Typical large scale top submerged injecting lances have an outer pipe diameter of 200 to 500 mm, or larger. Also, the lance is much longer and extends down through the roof of a top submerged lancing reactor that may be about 10 to 15 m tall, so that the lower end of the outer pipe is immersed to a depth of up to about 300 mm or more in a molten slag phase of the bath, but is protected by a coating of solidified slag formed and maintained on the outer surface of the outer pipe by the cooling action of the injected gas flow within. The inner pipe may terminate at about the same level as the outer pipe, or at a higher level of up to about 1000 mm above the lower end of the outer pipe. Thus, it can be the case that the lower end of only the outer pipe is submerged. In any event, a helical vane or other flow shaping device may be mounted on the outer surface of the inner pipe to span the annular space between the inner and outer pipes. The vanes impart a strong swirling action to an air or oxygen-enriched blast along that annulus and serve to enhance the cooling effect as well as ensure that gas is mixed well with fuel and feed material supplied through the inner pipe with the mixing occurring substantially in a mixing chamber defined by the outer pipe, below the lower end of the inner pipe where the inner pipe terminates a sufficient distance above the lower end of the outer pipe.
The outer pipe of the top submerged injecting lance wears and burns back at its lower end, but at a rate that is considerably reduced by the protective frozen slag coating than would be the case without the coating. However, this is controlled to a substantial degree by the mode of operation with top submerged lancing technology. The mode of operation makes the technology viable despite the lower end of the lance being submerged in the highly reactive and corrosive environment of the molten slag bath. The inner pipe of a top submerged injecting lance may be used to supply feed materials, such as concentrate, fluxes and reductant to be injected into a slag layer of the bath, or it may be used for fuel. An oxygen containing gas, such as air or oxygen enriched air, is supplied through the annulus between the pipes. Prior to submerged injection within the slag layer of the bath being commenced, the lance is positioned with its lower end, that is, the lower end of the outer pipe, spaced a suitable distance above the slag surface. Oxygen-containing gas and fuel, such as fuel oil, fine coal or hydrocarbon gas, are supplied to the lance and a resultant oxygen/fuel mixture is fired to generate a flame jet that impinges onto the slag. This causes the slag to splash to form, on the outer lance pipe, the slag layer that is solidified by the gas stream passing through the lance to provide the solid slag coating mentioned above. The lance then can be lowered to achieve injection within the slag, with the ongoing passage of oxygen-containing gas through the lance maintaining the lower extent of the lance at a temperature at which the solidified slag coating is maintained and protects the outer pipe.
A new top submerged injecting lance usually has relative positions for the lower ends of the outer and inner pipes that is an optimum for a particular pyro-metallurgical operating window determined during the design. The relative positions can be different for different uses of top submerged lancing processes. However, the length of any mixing chamber formed between the lower end of the inner pipe and that of the outer pipe progressively falls below an optimum for a given pyro-metallurgical operation as the lower end of the outer pipe slowly wears and burns back. Similarly, if there is zero offset between the lower ends of the outer and inner pipes, the lower end of the inner pipe can become exposed to the slag, and also being worn and subjected to burn back. At intervals, the lower end of at least the outer pipe needs to be cut to provide a clean edge to which is welded a length of pipe of the appropriate diameter, to re-establish the optimum relative positions of the pipe lower ends to optimise smelting conditions.
With both top blowing and top submerged injecting lances, there have been proposals for fluid cooling to protect the lance from the high temperatures encountered in pyro-metallurgical processes. Examples of fluid cooled lances for top blowing are disclosed in US patents:                U.S. Pat. No. 3,223,398 to Bertram et al.,        U.S. Pat. No. 3,269,829 to Belkin,        U.S. Pat. No. 3,321,139 to De Saint Martin,        U.S. Pat. No. 3,338,570 to Zimmer,        U.S. Pat. No. 3,411,716 to Stephan et al.,        U.S. Pat. No. 3,488,044 to Shepherd,        U.S. Pat. No. 3,730,505 to Ramacciotti et al.,        U.S. Pat. No. 3,802,681 to Pfeifer,        U.S. Pat. No. 3,828,850 to McMinn et al.,        U.S. Pat. No. 3,876,190 to Johnstone et al.,        U.S. Pat. No. 3,889,933 to Jaquay.,        U.S. Pat. No. 4,097,030 to Desaar.,        U.S. Pat. No. 4,396,182 to Schaffar et al.,        U.S. Pat. No. 4,541,617 to Okane et al.; and        U.S. Pat. No. 6,565,800 to Dunne.        
All of these references, with the exception of U.S. Pat. No. 3,223,398 to Bertram et al. and U.S. Pat. No. 3,269,829 to Belkin, utilise concentric outermost pipes arranged to enable fluid flow to the outlet tip of the lance along a supply passage and back from the tip along a return passage, although Bertram et al use a variant in which such flow is limited to a nozzle portion of the lance. While Belkin provides cooling water, this passes through outlets along the length of an inner pipe to mix with oxygen supplied along an annular passage between the inner pipe and outer pipe, so as to be injected as steam with the oxygen. Heating and evaporation of the water provides cooling of the lance of Belkin, while steam generated and injected is said to return heat to the bath.
U.S. Pat. No. 3,521,872 to Themelis, U.S. Pat. No. 4,023,676 to Bennett et al. and U.S. Pat. No. 4,326,701 to Hayden, Jr. et al. purport to disclose lances for submerged injection. The proposal of Themelis is similar to that of U.S. Pat. No. 3,269,829 to Belkin. Each uses a lance cooled by adding water to the gas flow and relying on evaporation into the injected stream, an arrangement that is not the same as cooling the lance with water through heat transfer in a closed system. However, the arrangement of Themelis does not have an inner pipe and the gas and water are supplied along a single pipe in which the water is vaporised. The proposal of Bennett et al, while referred to as a lance, is more akin to a tuyere in that it injects, below the surface of molten ferrous metal, through the peripheral wall of a furnace in which the molten metal is contained. In the proposal of Bennett et al, concentric pipes for injection extend within a ceramic sleeve while cooling water is circulated through pipes encased in the ceramic. In the case of Hayden, Jr. et al, provision for a cooling fluid is made only in an upper extent of the lance, while the lower extent to the submergible outlet end comprises a single pipe encased in refractory cement.
Limitations of the prior art proposals are highlighted by Themelis. The discussion is in relation to the refining of copper by oxygen injection. While copper has a melting point of about 1085° C., it is pointed out by Themelis that refining is conducted at a superheated temperature of about 1140° C. to 1195° C. At such temperatures lances of the best stainless or alloy steels have very little strength. Thus, even top blowing lances typically utilise circulated fluid cooling or, in the case of the submerged lances of Bennett and Hayden, Jr, et al, a refractory or ceramic coating. The advance of U.S. Pat. No. 3,269,829 to Belkin, and the improvement over Belkin provided by Themelis, is to utilise the powerful cooling able to be achieved by evaporation of water mixed within the injected gas. In each case, evaporation is to be achieved within, and to cool, the lance. The improvement of Themelis over Belkin is in atomisation of the coolant water prior to its supply to the lance, avoiding the risks of structural failure of the lance and of an explosion caused by injection of liquid water within the molten metal.
U.S. Pat. No. 6,565,800 to Dunne discloses a solids injection lance for injecting solid particulate material into molten material, using an un-reactive carrier. That is, the lance is simply for use in conveying the particulate material into the melt, rather than as a device enabling mixing of materials and combustion. The lance has a central core tube through which the particulate material is blown and, in direct thermal contact with the outer surface of the core tube, a double-walled jacket through which coolant such as water can be circulated. The jacket extends along a part of the length of the core tube to leave a projecting length of the core tube at the outlet end of the lance. The lance has a length of at least 1.5 meters and from the realistic drawings, it is apparent that the outside diameter of the jacket is of the order of about 12 cm, with the internal diameter of the core tube of the order of about 4 cm. The jacket comprises successive lengths welded together, with the main lengths of steel and the end section nearer to the outlet end of the lance being of copper or a copper alloy. The projecting outlet end of the inner pipe is of stainless steel that, to facilitate replacement, is connected to the main length of the inner pipe by a screw thread engagement.
The lance of U.S. Pat. No. 6,565,800 to Dunne is said to be suitable for use in the Hlsmelt process for production of molten ferrous metal, with the lance enabling the injection of iron oxide feed material and carbonaceous reductant. In this context, the lance is exposed to hostile conditions, including operating temperatures of the order of 1400° C. However, as indicated above with reference to Themelis, copper has a melting point of about 1085° C. and even at temperatures of about 1140° C. to 1195° C., stainless steels have very little strength. Perhaps the proposal of Dunne is suitable for use in the context of the Hlsmelt process, given the high ratio of about 8:1 in cooling jacket cross-section to the cross-section of the core tube, and the small overall cross-sections involved. The lance of Dunne is not a top submerged injecting lance, nor is it suitable for use in top submerged lancing technology.
Examples of lances for use in pyro-metallurgical processes based on top submerged lancing technology are provided by U.S. Pat. Nos. 4,251,271 and 5,251,879, both to Floyd and U.S. Pat. No. 5,308,043 to Floyd et al. As detailed above, slag initially is splashed by using the lance prior to initiating a pyro-metallurgical operation, for a period of top blowing onto a molten slag layer. The top blowing causes slashing of the slag to form a coating of slag on the lower extent of the lance with the slag coating being to solidified, by high velocity top blown gas that generates the splashing, to achieve a protective coating of solid slag on the lance. The solid slag coating is maintained during top submerged injection within the slag, despite the lance then being lowered to submerge the lower outlet end in the slag layer to enable the required top submerged lancing injection within the slag. The lances of U.S. Pat. Nos. 4,251,271 and 5,251,879, both to Floyd, operate in this way with the cooling to maintain the solid slag layer being solely by injected gas in the case of U.S. Pat. No. 4,251,271 and by that gas plus gas blown through a shroud pipe in the case of U.S. Pat. No. 5,251,879. However, with U.S. Pat. No. 5,308,043 to Floyd et al. cooling, additional to that provided by injected gas and gas blown through a shroud pipe, is provided by cooling fluid circulated through annular passages defined by the outer three pipes of the lance. This is made possible by provision of an annular tip of solid alloy steel that, at the outlet end of the lance, joins the outermost and innermost of those three pipes around the circumference of the lance. The annular tip is cooled by injected gas and also by coolant fluid that flows across an upper end face of the tip. The solid form of the annular tip, and its manufacture from a steel alloy, results in the tip having a good level of resistance to wear and burn back. The arrangement is such that a practical operating life can be achieved with the lance before it is necessary to replace the tip in order to safeguard against a risk of failure of the lance enabling cooling fluid to discharge within the molten bath.
Further examples of lances for use in top submerged lancing technology are provided in our co-pending applications WO2013/000,017, WO2013/029,092 and PCT/IB2012/056,714. The invention of WO2013/000,017 relates to a top submerged injecting lance having at least inner and outer substantially concentric pipes, with the relative positions of the outer pipe and a next innermost pipe being longitudinally adjustable to enable a mixing chamber at their lower outlet ends to be maintained at a desired setting during a period of use to compensate for wear and burn back of the lower end of the outer pipe. The invention of WO2013/029,092 relates to a top submerged injecting lance having at least inner and outer pipes, a shroud around and spaced from the outer pipe, with the shroud longitudinally adjustable relative to the outer pipe of the lance to enable maintenance of, or variation in, a longitudinal spacing between the outlet ends of the shroud and the outer pipe. The application PCT/IB2012/056,714 provides a top submerged injecting lance having provision for circulation of a coolant fluid, in which a constriction within the lower end of the lance causes an increase in fluid flow velocity between an end wall for a return flow of coolant fluid along an outermost pipe of the lance.
The pyro-metallurgical operations conducted with both top blowing and top submerged lancing injection generate very high bath temperatures, ranging up to about 1650° C. in extreme cases enabled by top submerged lancing technology. However, accurate determination of temperature in molten bath smelting processes is critical for control of the process and optimum operation. In some cases, it is necessary that the bath temperature be maintained within a relatively narrow range, while other operations need to be able to change from one bath temperature level to another, on changing between process stages. In any case operation at the lowest practicable temperature provides the most efficient operation in terms of cost and environmental footprint.
Traditionally bath temperatures have been measured or at least inferred by methods that involve use of:                (i) thermocouples that are mounted in a side wall of a reactor, and either embedded in, or protruding through, a refractory lining of a reactor vessel;        (ii) thermocouples that are placed in discharge launders or weirs;        (iii) an examination of the thickness of bath coatings frozen onto cold dip rods; and/or        (iv) port or roof mounted pyrometers.However, other, newer methods proposed include heat pipes, optical fibres and infrared techniques.        
The traditional methods have suffered from issues of high fixed and operating costs, reliability, inaccuracy and interference such as from opaque off-gases and fumes, although pyrometry via roof or port mounted pyrometers has proven to be useful in only some circumstances. Newer methods have yet to be proven reliable or commercially viable.
Optical thermometry based on infrared techniques have been utilised in a number of ways. A paper entitled “The Benefits of Fixed Thermal Imaging” by Kresch, published in 2010 in Process Heating Magazine, points out that the amount of radiated energy from an object is a function of the objects temperature and emissivity. Kresch indicates that a thermal imaging camera can identify hot or cold spots by measuring surface temperature variations, to enable adjustment of process parameters for greater productivity and throughput. In contrast, IR spot sensors are said to be capable of only a single-point temperature reading. Kresch envisages application of thermal cameras installed at appropriate points in an incinerator, to enable prevention of major fires caused by undetected burning garbage. Numerous other parties either have proposed or used thermal cameras to monitor a stream of steel as it is poured, to enable pouring to be terminated as soon as slag is detected in the stream.
A paper entitled “Incredible Infrared” by Canfield et al., published in Process Heating Magazine in January 2009, relates to the use of IR sensors that also measure emitted IR energy from a body, as a function of the temperature and emissivity of the body. However, in contrast to conversion of detected radiated energy to an image able to be presented on a screen, using a thermal camera, the IR sensors focus the emitted energy onto a detector that generates an electrical signal able to be amplified and displayed as a temperature reading. As with the thermal cameras, the sensors can be used with both fixed and moving objects or bodies. Canfield et al. refers to measuring the temperature of a coating applied to and being cured on continuous foil. It is said that the IR sensors can receive energy emitted from a large area or a small spot on an object. A similar article by Starrh, entitled “Spectral Manoeuvres” and published June/July 2007 in Industrial Automation Asia, pp. 53-54, in describing IR sensors or thermometers, discusses the importance of target size relative to the sensors field-of-view or spot size. The sensors are said to have a sensor to target distance to spot diameter able to vary from 2:1 models to a more expensive 300:1 model. The Starrh article also is illustrated by reference to a coating applied to and being cured on strip, in that instance in forming a laminate. Also, the Raytek website at www.raytek.com details, in “Success Story 64”, use of an IR sensor for measuring the temperature of a molten metal alloy under vacuum and needing to be held at a stable temperature for investment casting. Two sensors are used, to enable comparison of their outputs, and are said to reduce the number of dip probes an operator needs to use in order to check temperature from time to time.
These applications of IR thermal imaging cameras and IR sensors or thermometers have not been found to be suitable for use in measuring the temperature of a molten bath in a pyro-metallurgical process conducted by top submerged lancing technology. This is despite the fact that the papers by Kresch, Canfield et al. and Starrh, and Success Story 64, relate to temperature measurements varying from about 685° F. (about 365° C.) in Canfield et alto about 2730° F. (about 1500° C.) in Success Story 64. At least at the upper end, this range is applicable to pyro-metallurgical operations.
A Steel Project Fact Sheet, published by the Office of Industrial Technologies, Energy Efficiency and Renewable Energy, US Department of Energy, and published in February 2001, proposes optical sensors and controls for improved basic oxygen furnace (BOF) operations. The proposal is to mount an optical sensor at the tip of a lance by which oxygen is blown at supersonic velocity downwardly, from above a molten bath of pig iron and slag. The sensor mounted on the lance enables determination of a bulk temperature for the bath from the slag temperature, using optical image-based techniques, while oxygen is not being blown. Also, the sensor enables monitoring, during oxygen blowing, of hot spot emission from the iron where the supersonic oxygen displaces slag to expose a surface region of the iron. The arrangement additionally is said to provide for bath height measurement for improved lance operating practice during a blow, as well as to enable viewing of the furnace interior for assessment of wear and slag splashing.
Others have proposed the use of infrared optical sensors for temperature measurements in submerged arc smelting furnaces, such as for the production of titaniferous slags, as well as ferro-silicon and ferro-chromium alloys. However, this use principally has focussed on determining temperature profiles for electrodes formed in the furnace during smelting. See, for example, the papers by Farina et al entitled “Measurement of temperature profiles in electrodes for silicon metal production”, IAS'2004, Seattle, 2004, pp. 195-199, and Laohasongkram et al., entitled “Application of Thermal Detector by Infrared for Electrical Arch Furnaces Transformer”, ICCAS, Oct. 17-20, 2007, in Seoul, Korea.
The present invention relates to an improved temperature measuring apparatus for use in measuring the temperature of a molten bath of a top submerged lancing installation, in the course of conducting a pyro-metallurgical operation in the top submerged lancing installation.